[clang] [HLSL] Make casting functions constexpr (PR #108902)

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Mon Sep 16 17:19:34 PDT 2024


llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Chris B (llvm-beanz)

<details>
<summary>Changes</summary>

This marks the `bit_cast` helper as `constexpr` and allows the casts implemented with it to also be `constexpr`. This is largely not a functional change, but it enables using the casts in expressions that need to be resolved at compile time as demonstrated with the static asserts in the new tests.

---
Full diff: https://github.com/llvm/llvm-project/pull/108902.diff


5 Files Affected:

- (modified) clang/lib/Headers/hlsl/hlsl_detail.h (+5-5) 
- (modified) clang/lib/Headers/hlsl/hlsl_intrinsics.h (+4-4) 
- (modified) clang/test/CodeGenHLSL/builtins/asuint.hlsl (+6-6) 
- (added) clang/test/SemaHLSL/BuiltIns/asfloat-constexpr.hlsl (+10) 
- (added) clang/test/SemaHLSL/BuiltIns/asuint-constexpr.hlsl (+10) 


``````````diff
diff --git a/clang/lib/Headers/hlsl/hlsl_detail.h b/clang/lib/Headers/hlsl/hlsl_detail.h
index 9801d86208159f..40849dcdf187e4 100644
--- a/clang/lib/Headers/hlsl/hlsl_detail.h
+++ b/clang/lib/Headers/hlsl/hlsl_detail.h
@@ -13,23 +13,23 @@ namespace hlsl {
 
 namespace __detail {
 
-#define _HLSL_INLINE                                                           \
-  __attribute__((__always_inline__, __nodebug__)) static inline
-
 template <bool B, typename T> struct enable_if {};
 
 template <typename T> struct enable_if<true, T> {
   using Type = T;
 };
 
+template <bool B, class T = void>
+using enable_if_t = typename enable_if<B, T>::Type;
+
 template <typename U, typename T, int N>
-_HLSL_INLINE typename enable_if<sizeof(U) == sizeof(T), vector<U, N> >::Type
+constexpr enable_if_t<sizeof(U) == sizeof(T), vector<U, N> >
 bit_cast(vector<T, N> V) {
   return __builtin_bit_cast(vector<U, N>, V);
 }
 
 template <typename U, typename T>
-_HLSL_INLINE typename enable_if<sizeof(U) == sizeof(T), U>::Type bit_cast(T F) {
+constexpr enable_if_t<sizeof(U) == sizeof(T), U> bit_cast(T F) {
   return __builtin_bit_cast(U, F);
 }
 
diff --git a/clang/lib/Headers/hlsl/hlsl_intrinsics.h b/clang/lib/Headers/hlsl/hlsl_intrinsics.h
index 6a50d50ebd3479..12f58ef0718695 100644
--- a/clang/lib/Headers/hlsl/hlsl_intrinsics.h
+++ b/clang/lib/Headers/hlsl/hlsl_intrinsics.h
@@ -370,11 +370,11 @@ bool any(double4);
 /// \param Val The input value.
 
 template <typename T, int N>
-_HLSL_INLINE vector<float, N> asfloat(vector<T, N> V) {
+constexpr vector<float, N> asfloat(vector<T, N> V) {
   return __detail::bit_cast<float, T, N>(V);
 }
 
-template <typename T> _HLSL_INLINE float asfloat(T F) {
+template <typename T> constexpr float asfloat(T F) {
   return __detail::bit_cast<float, T>(F);
 }
 
@@ -415,11 +415,11 @@ float4 asin(float4);
 /// \param Val The input value.
 
 template <typename T, int N>
-_HLSL_INLINE vector<uint, N> asuint(vector<T, N> V) {
+constexpr vector<uint, N> asuint(vector<T, N> V) {
   return __detail::bit_cast<uint, T, N>(V);
 }
 
-template <typename T> _HLSL_INLINE uint asuint(T F) {
+template <typename T> constexpr uint asuint(T F) {
   return __detail::bit_cast<uint, T>(F);
 }
 
diff --git a/clang/test/CodeGenHLSL/builtins/asuint.hlsl b/clang/test/CodeGenHLSL/builtins/asuint.hlsl
index ac3dae26d6caed..252a434ccce0dc 100644
--- a/clang/test/CodeGenHLSL/builtins/asuint.hlsl
+++ b/clang/test/CodeGenHLSL/builtins/asuint.hlsl
@@ -1,40 +1,40 @@
 // RUN: %clang_cc1 -finclude-default-header -x hlsl -triple dxil-pc-shadermodel6.3-library %s -fnative-half-type -emit-llvm -O1 -o - | FileCheck %s
 
-// CHECK: define {{.*}}test_uint{{.*}}(i32 {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: define {{.*}}test_uint{{.*}}(i32 {{.*}} [[VAL:%.*]]){{.*}}
 // CHECK-NOT: bitcast
 // CHECK: ret i32 [[VAL]]
 uint test_uint(uint p0) {
   return asuint(p0);
 }
 
-// CHECK: define {{.*}}test_int{{.*}}(i32 {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: define {{.*}}test_int{{.*}}(i32 {{.*}} [[VAL:%.*]]){{.*}}
 // CHECK-NOT: bitcast
 // CHECK: ret i32 [[VAL]]
 uint test_int(int p0) {
   return asuint(p0);
 }
 
-// CHECK: define {{.*}}test_float{{.*}}(float {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: define {{.*}}test_float{{.*}}(float {{.*}} [[VAL:%.*]]){{.*}}
 // CHECK: bitcast float [[VAL]] to i32
 uint test_float(float p0) {
   return asuint(p0);
 }
 
-// CHECK: define {{.*}}test_vector_uint{{.*}}(<4 x i32> {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: define {{.*}}test_vector_uint{{.*}}(<4 x i32> {{.*}} [[VAL:%.*]]){{.*}}
 // CHECK-NOT: bitcast
 // CHECK: ret <4 x i32> [[VAL]]
 uint4 test_vector_uint(uint4 p0) {
   return asuint(p0);
 }
 
-// CHECK: define {{.*}}test_vector_int{{.*}}(<4 x i32> {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: define {{.*}}test_vector_int{{.*}}(<4 x i32> {{.*}} [[VAL:%.*]]){{.*}}
 // CHECK-NOT: bitcast
 // CHECK: ret <4 x i32> [[VAL]]
 uint4 test_vector_int(int4 p0) {
   return asuint(p0);
 }
 
-// CHECK: define {{.*}}test_vector_float{{.*}}(<4 x float> {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: define {{.*}}test_vector_float{{.*}}(<4 x float> {{.*}} [[VAL:%.*]]){{.*}}
 // CHECK: bitcast <4 x float> [[VAL]] to <4 x i32>
 uint4 test_vector_float(float4 p0) {
   return asuint(p0);
diff --git a/clang/test/SemaHLSL/BuiltIns/asfloat-constexpr.hlsl b/clang/test/SemaHLSL/BuiltIns/asfloat-constexpr.hlsl
new file mode 100644
index 00000000000000..b2a54d23173e57
--- /dev/null
+++ b/clang/test/SemaHLSL/BuiltIns/asfloat-constexpr.hlsl
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -finclude-default-header -triple dxil-pc-shadermodel6.6-library %s -verify
+
+// expected-no-diagnostics
+
+// Because asuint should be constant evaluated, all the static asserts below
+// should work!
+void ConstExprTest() {
+  static_assert(asfloat(0x3f800000) == 1.0f, "One");
+  static_assert(asfloat(0x40000000.xxx).y == 2.0f, "Two");
+}
diff --git a/clang/test/SemaHLSL/BuiltIns/asuint-constexpr.hlsl b/clang/test/SemaHLSL/BuiltIns/asuint-constexpr.hlsl
new file mode 100644
index 00000000000000..be6afda3be6636
--- /dev/null
+++ b/clang/test/SemaHLSL/BuiltIns/asuint-constexpr.hlsl
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -finclude-default-header -triple dxil-pc-shadermodel6.6-library %s -verify
+
+// expected-no-diagnostics
+
+// Because asuint should be constant evaluated, all the static asserts below
+// should work!
+void ConstExprTest() {
+  static_assert(asuint(1) == 1u, "One");
+  static_assert(asuint(2.xxx).y == 2u, "Two");
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/108902


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